1. Field of the Invention
This invention relates generally to electronic identification and recognition systems and more specifically to such systems wherein it is not necessary to make physical contact between the identification section and the reader section.
2. Description of the Prior Art
There are various electronic identification and recognition systems wherein the identifying device is portable. Sometimes the identifying device is referred to as a "card", "tag", "key", or the like. The recognition station or reader section is prepared to recognize identifying devices of predetermined characteristics when such identifying device is brought within the proximity of the reader section. One method used for proximity identification is by high frequency radio signals. These radio signals at 915 megahertz or 2.4 gigahertz can be identified by reflection and selective absorption methods. Problems with this approach include the cost of circuits and antennas, possible health hazards at the higher frequency, and null spots at intermediate distances. A second method for proximity identification is by inductive coupling. Here the inductive flux lines radiate from a coil or loop antenna in a reader section to a similarly shaped loop in the identification section. A problem with this method is that if the object to be identified includes a metal surface or metal walls, the flux path is attenuated and the range is reduced. Another problem with inductive coupling of the prior art is that the loop antennas tend to be quite large and bulky.
The prior art includes various patents and patent applications by the present inventor. The patents include U.S. Pat. No. 3,752,960 for "Electronic Identification and Recognition System", issued Aug. 14, 1973; U.S. Pat. No. 3,816,708 for "Electronic Recognition and Identification System", issued June 11, 1974; U.S. Pat. No. 3,816,709 for "Electronic Identification and Recognition System", issued June 11, 1974; U.S. Pat. No. 4,223,830 for "Identification System", issued Sept. 23, 1980; U.S. Pat. No. 4,236,068 for "Personal Identification and Signalling System", issued Nov. 25, 1980; U.S. Pat. No. 4,384,288 for "Portable Radio Frequency Emitting Identifier", issued May 17, 1983; U.S. Pat. No. 4,388,524 for "Electronic Identification and Recognition With Code Changeable Reactance", issued June 14, 1983; U.S. Pat. No. 4,459,474 for "Identification System With Separation and Direction Capability and Improved Noise Reduction", issued July 10, 1984; U.S. Pat. No. 4,473,825 for "Electronic Identification System With Power Input-Output Interlock and Increased Capabilities", issued Sept. 25, 1988; U.S. Pat. No. 4,546,241 for "Electronic Proximity Identification Systems", issued Oct. 8, 1985; U.S. Pat. No. 4,580,041 for "Electronic Proximity Identification System With Low Power Identifier, Simplified", issued Apr. 1, 1986; U.S. Pat. No. 4,600,829 for "Electronic Proximity Identification and Recognition System With Isolated Two-Way Coupling", issued July 15, 1986; U.S. Pat. No. 4,654,658 for "Identification System With Vector Phase Angle Detection", issued Mar. 31, 1987; and U.S. Pat. No. 4,656,472 for "Proximity Identification System With Power Aided Identifier", issued Apr. 7, 1987. In addition, there is currently pending a U.S. patent application Ser. No. 06/892,120 for "Proximity Identification System With Lateral Flux Paths", filed Aug. 4, 1986.